The invention relates to a method for controlling an internal combustion engine—especially for controlling an Otto engine in the event of torque interventions or in idling speed mode.
There already exist a plurality of different methods for controlling an internal combustion engine. Within the scope of an idling speed control of an Otto engine, the output engine torque for holding constant the rotational speed may be changed in both the negative (to reduce the speed) and the positive direction (to raise the speed). Therefore, any torque request that may arise is usually set by adjusting the ignition angle and changing the mass of air and fuel that is to be delivered. To be able to adjust the engine torque with high dynamics also in the positive direction, a so-called torque reserve is used. In so doing, the ignition angle is subsequently shifted in the retard direction in accordance with the torque-optimized ignition angle; and both the air mass to be supplied and also the fuel mass to be supplied are simultaneously increased (e.g., this method is used for controlling the torque with the torque reserve in the internal combustion engine of the BMW 520i model year 2004). Inside this torque reserve, the torque to be generated may be shifted very rapidly by shifting the ignition angle in the direction of the torque-optimized ignition angle. Short-term torque requests may be quickly balanced in this way, and result in only a slight decrease in the idling speed.
However, a torque reserve that is set accordingly results in an increase in the fuel consumption—especially when the internal combustion engine is in an idling mode.
The present invention is based on the problem of providing a method of the above described class that improves upon the amount of the torque reserve and the fuel consumption characteristics.
The invention solves this problem by providing a method for controlling an internal combustion engine operating homogeneously and having a control unit for setting an air mass supply, a fuel mass supply, and the ignition angle, wherein starting from a specific air-fuel ratio (λ) in the mixture, the air mass to be supplied is increased, and the mixture of air and fuel is leaned to generate a first torque reserve. In the event of a positive torque request, the fuel mass that is to be supplied for enriching the air-fuel mixture is increased.
Owing to the increase in the air mass and the thereby resulting leaning of the air-fuel mixture, a first torque reserve is generated; and then in the event of a positive torque request, the reserved torque is retrieved through the targeted increase in the fuel mass. In particular, a leaning of the mixture is achieved in that if the fuel mass that is made available for use and/or supplied is held constant (e.g., by holding constant the injection period), the air mass is increased. The result is that the output torque of the engine is not changed, but the air-fuel mixture is leaner; and at the same time a significant savings in fuel is achieved in the idle speed mode. Only on the basis of a torque request is the requested torque actually made available within a very short time by enriching the lean mixture of air and fuel to a value in the range of lambda=1. However, it is also contemplated to increase merely the air mass at a disproportionate rate to the fuel mass; then the result would be a simultaneous increase in the current engine torque.
A torque request arises, for example, on a routine basis in the idling mode, when in this case the servo-supported steering is actuated; or the consumers, like the air conditioning system, are switched on. The method, according to the invention, is especially suitable for adjusting an idling speed that is to be held constant. Other torque requests arise in the normal driving mode, when, for example, the gear is to be shifted in an automated manner. Even in the overrun mode a torque reserve is preferably always generated in order to be able to react, if possible without any delay, to the driver's corresponding wishes (load request). So that the torque reserve may be made available for use in all situations, in which a corresponding torque reserve is desired, the operation of the internal combustion engine is monitored by use of a number of different operating parameters, so that when the appropriate operating parameters that signal a pending retrieval of the torque are present, a torque reserve is generated. In all cases the method, according to the invention, guarantees an instantaneous response of the internal combustion engine, and a distinct savings in fuel is achieved, as compared to the prior art methods.
In an especially preferred embodiment of the invention, another torque reserve is achieved in that, if at the same time that the ignition angle is shifted in the retard direction, the fuel mass that is to be made available for use is increased as the air mass increases in an analogous manner. Therefore, if at a constant fuel mass a higher torque reserve is requested than is possible by increasing the air mass owing to the burning limit, the fuel mass is increased in a manner analogous to the air mass that also continues to increase; and at the same time the ignition angle is shifted in the retard direction.
In the event of a fast torque request (or rather in the event that a torque request is to be implemented quickly), the ignition angle is shifted then—viewed temporally—preferably in the early direction at constant lean lambda (lambda>1) until the respective torque-optimized ignition angle (corresponding to the lambda that is set) is set. Not until then is additional fuel supplied until a lambda in the range of lambda=1 is set.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.